关于UIImage方向的坑--imageOrientation

最近几天项目用到了关于照片选择和照相机获取图片,出现了一个关于方向的bug,就是在本地展示的时候是正常方向展示的图片,但是上传后却发现照片向右旋转了90度,然后上网各种查资料,终于找到了一个大概的解决方案.

UIImage有一个imageOrientation的属性，主要作用是控制image的绘制方向，共有以下8中方向:

//UIImageOrientation的定义，定义了如下几种变换
typedef enum
{
UIImageOrientationUp,            // default orientation

 UIImageOrientationDown,          // 180 deg rotation

 UIImageOrientationLeft,          // 90 deg CCW

UIImageOrientationRight,         // 90 deg CW

UIImageOrientationUpMirrored,    // as above but image mirrored along other axis. horizontal flip

UIImageOrientationDownMirrored,  // horizontal flip

UIImageOrientationLeftMirrored,  // vertical flip

UIImageOrientationRightMirrored, // vertical flip

} UIImageOrientation;

(UIImage *)imageWithCGImage:(CGImageRef)cgImage scale:(CGFloat)scale orientation:(UIImageOrientation)orientation NS_AVAILABLE_IOS(4_0);

该方面使用一个CGImageRef创建UIImage，在创建时还可以指定方法倍数以及旋转方向。当scale设置为1的时候，新创建的图像将和原图像尺寸一摸一样，而orientaion则可以指定新的图像的绘制方向。

下面是个解决应用图片旋转或颠倒的bug：

+ (UIImage *)fixOrientation:(UIImage *)aImage {

// No-op if the orientation is already correct
if (aImage.imageOrientation == UIImageOrientationUp)
return aImage;

// We need to calculate the proper transformation to make the image upright.
// We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
CGAffineTransform transform = CGAffineTransformIdentity;

switch (aImage.imageOrientation) {
case UIImageOrientationDown:
case UIImageOrientationDownMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);
transform = CGAffineTransformRotate(transform, M_PI);
break;

case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
transform = CGAffineTransformRotate(transform, M_PI_2);
break;

case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);
transform = CGAffineTransformRotate(transform, -M_PI_2);
break;
default:
break;
}

switch (aImage.imageOrientation) {
case UIImageOrientationUpMirrored:
case UIImageOrientationDownMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
transform = CGAffineTransformScale(transform, -1, 1);
break;

case UIImageOrientationLeftMirrored:
case UIImageOrientationRightMirrored:
transform = CGAffineTransformTranslate(transform, aImage.size.height, 0);
transform = CGAffineTransformScale(transform, -1, 1);
break;
default:
break;
}

// Now we draw the underlying CGImage into a new context, applying the transform
// calculated above.
CGContextRef ctx = CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,
CGImageGetBitsPerComponent(aImage.CGImage), 0,
CGImageGetColorSpace(aImage.CGImage),
CGImageGetBitmapInfo(aImage.CGImage));
CGContextConcatCTM(ctx, transform);
switch (aImage.imageOrientation) {
case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
// Grr...
CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);
break;

default:
CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);
break;
}

// And now we just create a new UIImage from the drawing context
CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
UIImage *img = [UIImage imageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
return img;
}